In a method of processing a silver halide color photographic material, in general, the used processing solutions are drained as overflow wastes.
However, such used processing solutions to be recovered or drained as overflow wastes have high environmental pollution load values. In addition, it is expensive to recover and collect the waste solutions. On the other hand, if the used processing solutions (overflow liquids) could be re-used as replenishers to the processing system, the above problem could be solved and, additionally, the active components remaining in the overflow liquids could also be re-used. As a result, the amount of chemicals needed for producing fresh replenishers could be reduced to thereby reduce processing costs. Accordingly, various techniques of recovering and regenerating used processing solutions have heretofore been studied in this technical field. For example, the fluctuation in the concentration of the components in the used processing solution as recovered is compensated in such a way that the compensated solution can be re-used as a replenisher. For the compensation, in general, accumulated components which would adversely affect the photographic properties of the material to be processed are removed, while the consumed active components are supplemented, such that the thus compensated solution may be re-used as a replenisher.
Various investigations have been made of such regenerating techniques for a bleach-fixing solution for use in processing color photographic materials.
A bleach-fixing solution contains, in general, at least three chemicals each having a different function, including an aminopolycarboxylato/iron(III) complex as a bleaching agent, a thiocyanate as a fixing agent, and a sulfite as a preservative. The overflow from such a bleach-fixing solution contains, in addition to the three starting reagents, silver ion formed by desilvering the photographic material and color developer components carried over from the previous bath. Furthermore, the used bleach-fixing solution also contains an aminopolycarboxylato/iron(II) complex formed by oxidation of silver into silver ion.
As discussed above, the technique of regenerating the overflow from the used bleach-fixing solution generally includes removal of the harmful accumulated components and addition of consumed active components. In particular, the efficient removal or reduction of harmful accumulated components from the overflow is a problem. As a means of solving the problem, various regenerating methods have been proposed as discussed below, in which silver ion formed by desilvering is removed or reduced.
Radiography, 29, 256-259 (1963) and JP-A-48-3624 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") illustrates a method of contacting a used bleach-fixing solution with metallic iron (e.g., steel wool), in which the silver ion is recovered as metallic silver by contact with the metallic iron, such that the silver ion concentration in the used bleach-fixing solution is reduced. In this method, however, the metallic iron dissolves into the solution as iron(II) ion having a strong reducing power. As a result, the oxidizing power of the bleach-fixing solution is lowered to often cause inadequate desilvering or color-reproducibility. If, in this method, the silver ion concentration is further lowered, the problem becomes more severe.
JP-A-50-98837, JP-A-51-19535 and JP-A-51-36136 and U.S. Pat. No. 4,014,764 propose a method of reducing and recovering silver ion by electrolysis. Also in this case, the existing iron(III) complex is reduced to the corresponding iron(II) complex, and the sulfite ion is oxidized to a sulfate ion at the anode to also cause inadequate desilvering and color reproducibility. In addition, the stability of the bleach-fixing solution is thereby lowered. The above noted problems become more severe when the current amount is increased to thereby increase the silver recovery percentage and lower the silver ion concentration in the bleach-fixing solution.
J. Appl. Photogr. Eng., 6, 14-18 (1980) and PMPTE J., 93, 800-807 (1987) mention a technique of adsorbing and removing the remaining silver complex by the use of an ion exchange resin. In accordance with this method, however, the adsorbed silver complex must be desorbed from the resin and the resin must be regenerated. For such desorption and regeneration, a complicated operation is necessary. In addition, a large amount of waste is drained from the process, and the operating cost is unsatisfactorily high.
JP-B-48-33697 (the term "JP-B" as used herein means an "examined Japanese patent publication") and JP-A-50-145231 propose a method of regenerating an overflow not by positively removing silver, but by reducing the relative amount of the equilibrated accumulation of silver ion by dilution. The method does not require any particular silver recovering device and recovery of silver for re-use is possible by this method. Therefore, the method is simple and inexpensive. In accordance with this method, however, silver halide eluted from the processed photographic material as well as sulfates accumulate in the processing solution. In particular, when a large amount of silver bromide is eluted, the accumulated halide and sulfate cause desilvering delay. In addition, because of the accumulation of developer components, the processed photographic material would have undesirable staining, and the color reproduction in the processed material would often be insufficient. Because of these reasons, the stability of photographic properties in continuous processing of this method is unsatisfactory.
In general, in the technique of regenerating and re-using the used processing solution by removing or reducing the concentration of harmful components in the used processing solution, it is difficult to finally control the proportion of the components in the regenerated solution. Therefore, there is an inevitable disadvantage in that the equipment for such regeneration is of large scale. Conventional methods of removing or reducing silver ion for re-use of the used bleach-fixing solution by the above-described prior art techniques were further found to have other additional disadvantages of the above-described desilvering and color reproducing insufficiency, in addition to control of the proportion of components in the regenerated solution.
Where a used bleach-fixing solution is regenerated and re-used, halide ion and silver ion accumulate, aminopolycarboxylato/iron(II) complexes accumulate, and additionally developer components and sulfates formed by oxidation of sulfite ion accumulate. The thus accumulated components can interact with each other in a complex manner to cause desilvering delay or leucoation of cyan dyes (as a result, insufficiency of color reproducibility). Such disadvantageous phenomena become pronounced in the case of rapid processing.
In a photographic laboratory, in general, plural processors are mostly used, and separate replenishers are generally applied to each of the processors. In this case, each of the processors is operated under different processing conditions (for example, with respect to the amount of the photographic material to be processed, the processing time, the processing temperature, etc.) and, as a result, the compositions of the respective tank solutions or the respective overflows are generally different from one another. In particular, the overflow from a first used bleach-fixing solution has different concentrations of preservative, silver ion and bleaching agent as compared to the overflow from a second processor. Where a plural number of such solutions is gathered and regenerated as a whole, the composition of the regenerated replenisher noticeably fluctuates. Because of such great fluctuation of the regenerated replenisher, the processed photographic material is undesirably stained (in the white background part), or desilvering of the processed photographic material is insufficient. Thus, the regeneration of overflows from plural tanks is much more difficult than the regeneration of one overflow from a single tank.
Because of the above reasons, regeneration of an overflow solution from a system of processing photographic materials is extremely difficult and, in particular, regeneration of an overflow solution from the bleach-fixing tank is most difficult.